1. Field of the Invention
The present invention generally relates to a method of making a photo-electric converting element having an elongated configuration or a large surface area, and more particularly, to a method of making the photo-electric converting element suited for use as a contact-type image sensor.
2. Description of the Prior Art
The use of amorphous silicon or the like has been suggested as a material for an electroconductive thin-film for use in the manufacture of an elongated image element. However, since the output signal current is very weak, a storage-type read-out system is employed. In order to attain high-speed operation in this system, switches for selecting pixels must be used for each pixel, and therefore, the use of the plural switches renders the manufacturing cost high.
On the other hand, a contact-type image sensor utilizing photoconductive layers of CdS, CdSe or the like can give a sufficiently high signal output, and therefore, not only can a real-time read-out system be employed therefor, but a matrix drive system can also be used for driving the image sensor. This in turn brings about an advantage in that the number of switching elements required can be reduced.
However, the formation of the photoconductive layer of CdS, CdSe or the like by the use of the known vacuum deposition technique has a problem in that deviation from the stoichiometric composition tends to vary with the manufacturing conditions, with the consequence that the reproducibility thereof is lowered.
When the photoconductive layer is formed by the use of a sintering technique wherein the photoconductive layer is formed by sintering on an electrode pattern which has been formed on the substrate, not only must the material for the electrodes be of a type having such a high heat resistance as to withstand the atmosphere in which it is subsequently activated, but also it is difficult to keep good contact between the photoconductive layer and the electrodes. Moreover, since the photoconductive layer formed by the vacuum deposition technique has its peripheral edge steeply inclined from the glass substrate, not only is it difficult to use a lift-off technique in the formation of the electrodes, but also portions of the electrodes between the photoconductive layer and the substrate tend to be broke off, causing the electric connection to fail with an external circuit.